Integrated circuits typically include buffer circuits therein for driving on-chip and off-chip loads. Dynamic output control (DOC) can also be provided by output buffers, such as those disclosed in application notes by Texas Instruments, Inc. (see, http://www.ti.com/sc/AVC). In particular, these output buffers having DOC circuitry may provide variable output impedance to reduce signal noise during output transitions. In these buffers, the DOC circuitry is stated as providing enough current to achieve high signaling speeds, while also having the ability to quickly switch the impedance level to reduce the undershoot and overshoot noise that is often found in high-speed logic. Such DOC circuitry may be used advantageously to eliminate the need for damping resistors which can limit noise but typically also increase propagation delay.
Additional buffer circuits are also disclosed in U.S. Pat. No. 5,894,238 to Chien, entitled "Output Buffer With Static and Transient Pull-Up and Pull-Down Drivers". In particular, the '238 patent discloses an inverting buffer circuit that utilizes a signal fed back from an output node (DOUT) through logic gates to control the transfer of data input signals (OL or /OH) to inputs of a transient driver circuit containing an NMOS pull-down transistor 22 and a PMOS pull-up transistor 12.
Notwithstanding such conventional output buffers with DOC circuitry, however, there still exists a need for output buffers that have excellent noise, propagation delay and impedance matching characteristics.